The increasing carbon dioxide concentration in the atmosphere and the resulting greenhouse effect and climate change have become compelling topics for scientific research. In order to understand the global carbon balance, it is necessary to determine the rate at which carbon dioxide and energy exchanges between the atmosphere and terrestrial and oceanic ecosystems. A measurement technique called xe2x80x9ceddy covariancexe2x80x9d has been widely used to determine these rates. The air just above the earth""s surface is turbulent, and small parcels of air called xe2x80x9ceddiesxe2x80x9d transport carbon dioxide, water vapor, and heat between the atmosphere and the surface. These transport rates can be calculated from simultaneous, high-frequency measurements of the vertical component of wind speed, the concentrations of carbon dioxide and water vapor, and the air temperature.
To measure concentrations of carbon dioxide and water vapor, a gas analyzer can be used to analyze the transmittance of light in appropriate wavelength bands through a gas sample. With some gas analyzers, a sample gas containing unknown gas concentrations of carbon dioxide and water vapor is placed in a sample cell, and a reference gas with zero or known concentrations of carbon dioxide and water vapor is placed in a reference cell. The analyzer measures the unknown gas concentrations in the sample cell from calibrated signals that are proportional to the difference between light transmitted through the sample cell and light transmitted through the reference cell.
In eddy covariance applications, ambient air that is full of dust and pollen must be moved through the analyzer at high flow rates in order for the analyzer to have the necessary frequency response. Even when the air is filtered, contamination of the sample cells is inevitable, requiring the analyzer to be returned to the factory for cleaning. This is an expensive and time-consuming process, especially when the analyzer is used in a remote location such as the Amazon basin, the north slope of Alaska, or the deserts of Africa.
There is a need, therefore, for an improved gas analyzer.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims.
By way of introduction, the preferred embodiments described below provide an improved gas analyzer that overcomes the problems described above. In one preferred embodiment, a gas analyzer is presented that focuses light beams through gas cells without reflecting the light beams off the walls of the cells. By eliminating wall reflections, dirt or debris on the walls of the cells will not result in inaccurate gas concentration measurements. In another preferred embodiment, a gas analyzer is disclosed having removable gas cells, which allows a user to easily clean the cells instead of returning a contaminated gas analyzer to service personnel for disassembly, cleaning, and re-assembly. In yet another preferred embodiment, a gas analyzer with a purged gas flow channel is described. In this preferred embodiment, purged gas flows between source and detector sections of the analyzer, ensuring that the source and detector sections are free of contaminants that can result in inaccurate gas concentration measurements. In an additional preferred embodiment, a gas analyzer is disclosed which has a heat exchanger to equilibrate the temperature of incoming air to the temperature of the analyzer""s gas cells, thereby avoiding temperature-based errors in gas concentration measurements.
The preferred embodiments will now be described with reference to the attached drawings.